We have constructed various baculovirus recombinants expressing selected rotavirus proteins including VP4 (P1A, P1B, P2, P3, P4, P5B, P6 or P7), VP7 (G1, G2, G3, G4, G6 or G9) or NSP4 (genotype A, B, C or D). By using immunocytochemistry assay involving such recombinants, we analyzed sera from (i) gnotobiotic piglets or calves infected orally with selected human (HRV) or animal rotaviruses or (ii) infants who received oral attenuated rotavirus vaccine. We showed that (i) in primary infections in animals, IgG antibody responses to homotypic VP4 or VP7 were significantly higher than those to heterotypic VP4s or VP7s, (ii) heterotypic responses in animals to HRV VP4s (P1A, 1B, 2A, 3 or 4) induced by rhesus RRV VP4 (P5B) or bovine UK VP4 (P7) were of low titer or infrequent, (iii) in primary infection in animals with HRV D (genotype B) or RRV (genotype C), antibody responses to homotypic NSP4 were significantly higher than those to heterotypic NSP4s, (iv) a single dose of monovalent HRV M37 (P2A,G1)or bovine NCDV (P6,G6) vaccine, or three doses of quadrivalent bovine rotavirus (UK) (P7,G1,2,3 and 4) induced predominantly homotypic IgA antibody responses in infants and (v) the VP4-specific serum IgA antibody titers in infants determined by the immunocytochemistry assay did not correlate with the serum neutralizing antibody titers determined by a plaque reduction assay, but did correlate with the detection of serum antibody responses determined by an immunostaining assay.